The present invention relates generally to printing machines, and more particularly, is directed to a doctor blade having an integral tape seal thereon for use in such printing machines.
Conventionally, in printing machines, such as flexographic printing machines, an ink transfer or anilox roll transfers ink to an adjacent plate roll for printing. Ink is supplied to the anilox roll from an ink chamber defined by a chamber housing which partially surrounds the anilox roll. Specifically, ink is supplied through an ink supply tube and then through an ink supply line in the chamber housing, into the ink chamber. In like manner, ink is removed from the ink chamber through an ink return line in the chamber housing and then through an ink return tube.
In order to prevent the escape of ink from the chamber, while ensuring that the ink enters the cells in the anilox roll and has a predetermined thickness on the anilox roll, doctor blades are provided at the entry and exit positions of the anilox roll relative to the ink chamber. The doctor blades are fixed to the chamber housing by bolts so that the doctor blades overhang the chamber housing and contact the anilox roll.
With this arrangement, the outer surface of the anilox roll passes through the ink chamber and picks up ink for printing. The ink is metered by means of the doctor blades held to the inlet and outlet ends of the chamber housing, with the free ends of the doctor blades being in contact with the outer surface of the anilox roll. The doctor blades are clamped to a chamber housing by a clamp holder. However, the housing is typically made of metal so that the seal of the doctor blade to the metal housing is not good, that is, ink always migrates between the doctor blade and the housing, making it difficult to clean. In some instances, in order to prevent migration of ink past the doctor blades, O-ring seals are provided in recesses of the chamber housing, in contact with the doctor blades. However, such external O-ring seals are not entirely satisfactory in performance with respect to sealing of the doctor blades to prevent migration of the ink along the doctor blades, that is, with most clamping assemblies, ink migrates past the doctor blades.
Further, over time, the doctor blades and seals become caked with ink and/or wear out. As a result, the doctor blades and O-ring seals become ineffective for the above purposes, and must be changed. Thus, there is a requirement to change both the doctor blades and the O-ring seals, usually at different times. In addition, changing of the O-ring seals can be difficult and burdensome.
Although doctor blades are known which have a coating thereon, such coatings are not effective for providing a seal to prevent migration of ink along the doctor blades.
For example, U.S. Pat. No. 2,837,024 to Dougan is directed to an offset press having an ink fountain blade with slots therein, thus effectively providing a plurality of side-by-side doctor blade segments. The different doctor blade segments separated by the slots can be individually biased by different amounts so that different amounts of ink can be placed on the roll at different positions corresponding thereto.
A continuous sheet of a thin, resilient material extends at least from the metering edge of the blade back to a position close to the rear edge of the blade. The resilient material may be a synthetic rubber or a suitable resilient plastic which is resistant to petroleum base solvents and varnishes such as are used in ink manufacture and in the cleanup of the press. The rubber is vulcanized to the steel of the blade. The primary purpose of the rubber is to prevent leakage of ink between the slots.
However, in order to prevent ink from escaping through the slots, the rubber layer must extend to the surface of the ink roll, and therefore, be in contact with the ink roll. If the rubber layer is spaced away from the doctoring edge, it would permit ink to pass through the slots, and therefore, would be inoperative for its intended purpose.
However, to obtain accurate metering of the ink, only the metal or plastic portion of the doctor blade should be in contact with the anilox roll.
U.S. Pat. No. 2,313,830 to Lundbye discloses a doctor blade formed by a thin steel blade having a layer of graphite secured along its undersurface. However, the graphite compound extends to the doctoring edge, and is in fact the edge in contact with the ink roll. The purpose thereof is to prevent wear and scratching of the ink cylinder, and the function of such graphite layer is not to provide any sealing function.
Japanese Patent Publication No. 56-101853 discloses a doctor blade comprised of a soft fluorine rubber plate or polyamide plate and a firm steel, polyester or polycarbonate plate secured therewith by screws, adhesives or the like. As with Lundbye, the soft fluorine rubber plate or polyamide plate extends to the doctoring edge, and is in fact, in contact with the ink roll, for the same purpose as in Lundbye.